The structuralist lens breaks down a story into its component parts: the signifiers, which are the surface-level pieces of the text, and the signified, the concepts symbolized and represented by them. It highlights the inherent arbitrariness with which the signifiers connect to the signified, the rules with which the signs (the combination of signifier and signified) are organized, and the binary oppositions which often exist between the signs (and the contradictions, combinations, and resolutions that exist at the fringes of these binaries).
[Image description: John stands in his bedroom with a neutral expression. We see the dresser with its three drawers, with the cake and Dad’s note atop it. We see the Problem Sleuth poster above the dresser. John’s bedroom door, to the right, with the SBURB poster on it. To the right of the door, John’s bed, with a poster hanging on the wall above it. We see the CD rack at John’s feet. The captalogue card containing the rolled-up poster appears in the top left, on top of the two previous cards (whose contents are not visible). The captchalogue deck appears at the bottom of the screen.]
Here, we see that this poster (perhaps like the cakes?) is a BIRTHDAY ARTIFACT. The term ‘BIRTHDAY ARTIFACT’, which has not appeared before and (IIRC) does not appear again, is somewhat arbitrary. Many words could have replaced ‘artifact’. It is the proximity to ‘birthday’ that gives it meaning; this item is important because of why and when John has received it. He has not yet seen the poster, but its importance is guaranteed by the context within which it was received. Like Schrödinger’s proposed cat, the poster could be of interest to John, or it might not be, which he won’t know until he unrolls it.
This is itself suggestive of a binary opposition in Homestuck: BIRTHDAY ARTIFACTS, objects which are important because they are inherited from guardians or ancestors, and INTERESTS, things that characters care about because of something specific to their personalities or natures as individuals. John doesn’t know if he likes this poster, and he doesn’t enjoy the cakes. It’s worth keeping an eye out on which things are of interest to John, and which are instead artifacts which he has inherited.